Method for producing a pattern on a transparent substrate

ABSTRACT

The invention concerns a method for producing a pattern on a transparent substrate, particularly a glass or glass-ceramic substrate. 
     According to the invention, there is deposited on at least one area of one face of the substrate, a first layer of a photosensitive resin comprising at least one sensitizing agent and at least one photosensitive compound essentially composed of a polymer with an average degree of cross-linking d° such that it is able to absorb solid particles. Certain areas of said first layer are exposed to light, particularly in order to increase, in a controlled manner, the average degree of cross-linking do of said polymer so as to modulate its absorption capacity. On the first layer is deposited at least one second layer of a mineral-particle-based composition. The substrate is subjected to at least one treatment cycle, particularly in order to fix said mineral particles. 
     The invention also concerns the substrate produced by this method and its applications.

This is a division of application Ser. No. 09/118,816 filed on Jul. 20,1998 now U.S. Pat. No. 6,183,939.

BACKGROUND OF THE INVENTION

This invention concerns a method for producing a pattern on atransparent substrate, particularly a glass or glass-ceramic substrate,and also a substrate produced by this method.

It is well known from the prior art to use enamels to produce adecorative pattern on a glass or glass-ceramic substrate.

The enamels used for this application are generally obtained from whatis known as an enamel composition, comprising a powder essentiallycomposed of at least one glass frit (which acts as a vitreous matrix)and pigments as colorants in particular, the glass frit and the pigmentsbeing metal-oxide-based, and a medium permitting the application of theenamel composition to the substrate and its temporary adhesion thereto.The medium selected, depending on the intended use of the enamel, mustensure the satisfactory placing in suspension of the frit particles andpigment particles used and must be consumed during the baking of theenamel. This medium can include solvents, diluents, oils, resins, etc.

It is known to deposit these enamels by various printing techniques,most particularly by screen-printing techniques using a fabric whosemesh count and mesh openings depend on the pattern to be produced. Theseprinting techniques are very advantageous from an economic point ofview, in that they can be used for high-speed mass production. Inaddition, they are very well suited to the reproduction of large-sizeddecorative patterns on substrates of the types used by glassmakers.

These techniques are not completely satisfactory, however, particularlyin terms of flexibility of use and esthetics.

First, in order to change the pattern for reproduction it is necessaryto change the screen-printing cloth, which is tedious in industrialoperations, especially in “personalized” small-series production.

Second, the screen-printing technique itself leaves a grid that betraysthe original visible in the decorative pattern. Visually, the substrateprovided with the gridded pattern has something of the appearance of apiece of fabric.

It is also known from the prior art, for decorative applications on asubstrate made of any desired material, particularly the formation of acolored visible image, to use photosensitive resins as vehicles forpigments or colorants.

For such applications, it is known to employ two different approaches tothe use of these photosensitive resins.

The first approach consists in incorporating the desired ingredient(pigment or colorant) directly into the composition containing thephotosensitive resin, then exposing the resin through a positive ornegative plate by means of a UV lamp, and finally stripping [it] with anappropriate solvent to produce an insoluble image containing saidingredient on the substrate.

Moreover, this stripping step is cumbersome and complex, especiallysince it is necessary to find a perfect affinity between the solventused and the resin and to master the operating conditions, especiallywith respect to duration.

The second approach consists in first exposing the photosensitive resinin the same manner as above, then causing the pigment(s) to be absorbeddirectly by the portions of said resin not exposed to light, and finallystripping the resulting system with an appropriate solvent.

Apart from the fact that these two approaches have in common that theyare not suitable for large decorative patterns, most particularlybecause it is difficult to achieve an even distribution of the pigmentsover the entire surface of the substrate, they also have the majordisadvantage of not yielding long-lasting products, since the pigmentsor colorants tend to separate from the substrate.

SUMMARY OF THE INVENTION

The aim of the invention is, therefore, to correct the aforesaiddisadvantages, and in particular to propose a new method for producing apattern on a transparent substrate, particularly a glass orglass-ceramic substrate, adaptable to both small- and large-scaleproduction, and yielding a particularly esthetic, very-high-definition,durable pattern with no adverse effect on production cost.

To accomplish this aim, the object of the invention is a method forproducing a pattern on a transparent substrate, particularly a glass orglass-ceramic substrate.

According to the invention, the following steps are performed,particularly in succession:

a) On at least one area of one face of the substrate is deposited afirst layer of a photosensitive resin comprising at least onesensitizing agent and at least one photosensitive compound essentiallycomposed of a polymer with an average degree of cross-linking d° suchthat it is able to absorb solid particles,

b) Certain areas of said first layer are exposed to light, particularlyin order to increase, in a controlled manner, the average degree ofcross-linking do of said polymer so as to modulate its absorptioncapacity,

c) On said first layer is deposited at least one second layer of amineral-particle-based composition,

d) Said substrate is subjected to at least one treatment cycle,particularly in order to fix said mineral particles.

DETAILED DESCRIPTION OF THE INVENTION

Within the context of the invention, “pattern” is understood to meananything capable of modifying the appearance and/or structure of thebare transparent substrate, whether by imparting to it a particulareffect; by lending it an ornamental appearance in the form of anillustration, optionally for purposes of identification; or by providingit with other functions. Some of these other functions will be itemizedhereinbelow.

In the context of the invention, “mineral particles” is understood tomean any reflective mineral element whose index of refraction is verydifferent from that of the bare transparent substrate.

Similarly, it should be understood that at least one portion of the“mineral particles” modifying the appearance and/or structure of thebare transparent substrate serves as a binding agent whose melting pointis below the temperature to which the substrate is exposed.

The step of “fixing of the mineral particles” —Step d) according to theinvention—can be temporary or final, depending on the type of treatmentwhich the substrate is to undergo.

Thus, temporary fixing is achieved, for example, by ultraviolet (UV)treatment, which hardens the entire layer of photosensitive resindeposited.

This type of treatment furnishes a number of advantages.

Since the substrate becomes easy to handle, it can be transported beforethe final fixing of the mineral particles according to the invention.

Furthermore, this treatment makes it possible to achieve absolutesurface evenness of the layer of photosensitive resin, which may provenecessary in particular if another layer of the same type issuperimposed, as will be described hereinbelow.

Similarly, the final fixing of the mineral particles can be accomplishedby means of a heat treatment cycle. In this case, it is the above-citedportion serving as a binding agent that melts during this same heattreatment cycle.

Obviously, as will be described hereinbelow, a variant of the inventioncan consist in that all the mineral particles melt during the heattreatment cycle of Step d).

Such is the case, for example, with a so-called low-melting-point glassfrit, i.e., one whose melting point is below the temperature ofdeformation of the substrate, i.e., in most cases less than 750-800° C.,generally below 650° C.

In this particular case a decorative pattern with a sandy effect isobtained (the glazed surface being more or less diffusive).

It should be noted at the outset that within the context of theinvention, “glassfrit” is understood to mean a substantiallytransparent, vitrifiable composition in the form of a pigment-free,metal-oxide-based powder.

According to the invention, the phrase “a polymer with an average degreeof cross-linking d° such that it is able to absorb solid particles”means that a polymer is selected whose network is initially loose sothat the mineral particles can be inserted temporarily. In other words,this ensures satisfactory compatibility between the interstices in thenetwork of the polymer and the size of the particles selected.

When the exposure to light is performed selectively, the network isrendered more or less dense in the areas concerned, which then becomemore or less leaktight, so to speak, to the mineral particles.

The principal advantage of thus depositing a mineral-particle-basedcomposition by a photosensitization technique, compared to pressuredeposition techniques of the kind used in screen printing, lies in thefact that the quantity of mineral particles, as previously defined, canbe varied in a uniform manner over the entire glazed surface concerned.This results in the production of a particular decorative pattern, aneffect that could never be achieved with the pressure techniques, inwhich all points in the pattern are necessarily of the same intensity.Moreover, no trace of gridding appears in the decorative pattern.

An advantageous consequence of the method according to the invention isthat it is easy to implement and is low-cost in terms of money and time,since the operating conditions require no special precautions apart fromsolid mastery of Step b) involving the exposure to light, in order toobtain the desired variation of the absorption capacity of the polymer,and thus to achieve gradations within the gray scale by modifying thequantity of mineral particles absorbed.

Secondarily, the method according to the invention makes it possible to“personalize” the decorative pattern as desired, without the need forlengthy and painstaking preparation of a specialized tool or tools—nosmall advantage in an industrial setting.

The sensitizing agent selected is preferably a benzothiazole ornaphthothiazole derivative, or optionally, to broaden spectralsensitivity, an anilinovinyl heterocyclic ammonium salt. Further, saidsensitizing agent is preferably 1-N (methylbenzothiazolylidene)methyldithioacetate.

When this sensitizing agent is used in combination with the polymer asdefined above, its sensitivity interval is extended to a wavelength ofabout 0.5 micron, i.e., beyond the ultraviolet range (the upper limit ofwhich is 0.38 μm). Thus it is no longer necessary to select a highlyspecialized radiation source in order to perform Step b).

Advantageously, the polymer that has proven to be the most appropriatefor absorbing the finely ground mineral particles is ethylene-glycol andbutanediol polycynamylidene malonate.

Three variants can be envisioned for the performance of Step b) of themethod according to the invention:

According to the first variant, the exposure to light is effected bymeans of a radiation source, particularly an ultraviolet source, thatilluminates the entire surface of a plate reproducing the decorativepattern and superimposed on the first layer,

According to the second variant, the exposure to light is effected bythe projection of an image,

According to the third preferred variant, the exposure to light iseffected by means of a point radiation source, particularly anultraviolet point radiation source, preferably a laser, whose beamsweeps certain areas of the first layer.

With this third preferred variant it is possible to have very pronouncedgradations at highly localized sites within the pattern, since theexposure to light is effected point by point. In addition, it ispossible to “guide” the laser by means of a programmable logic unitaccording to the decorative pattern to be produced, which confersflexibility of use when the method according to the invention is used inan industrial production line.

According to a highly advantageous characteristic, the choice of thesize of the mineral particles, which is adapted primarily to theabsorption capacity of the polymer as noted above, is guided by thethickness of the first layer in such a way that the diameter of theparticles is less than or equal to this thickness.

For this purpose, the mineral particles are ground very finely, thegrind being finer, the higher the desired contrast between the differentportions of the decorative pattern and/or the desired resolution of thepattern. Thus, a lower particle diameter d₉₀ of 10 μm or less,preferably between 4 and 8 μm, is especially preferred, since itcorresponds well to the different thicknesses of the layers ofphotosensitive resin once they have been deposited and dried.

Similarly, the particle diameter d₁₀ selected is preferably between 0.2μm and 1 μm, and, further, diameter d₅₀ is preferably between 1 μm and 4μm. It will be recalled that these terms, “d₉₀,” “d₅₀” and “d₁₀,”signify that respectively 90%, 50% and 10% of the mineral particles inquestion have a diameter smaller than the indicated value. The d₉₀ valuegives a clear idea of the size of the particles. In conjunction with thevalues of d₁₀ and/or d₅₀, it provides a complete picture of the particlesize distribution within a given range of diameters.

In regard to Step d), the substrate is preferably subjected to a heattreatment cycle for the mineral particles, at temperatures equal to orgreater than the melting points of these particles, particularly between300 and 750° C., and further, preferably in the vicinity of 620° C.

In any event, the photosensitive resin should be eliminated attemperatures below those required to melt the mineral particles.

The aforesaid heat treatment cycle is advantageously part of aquenching, annealing or bending cycle.

The fixing temperature of the mineral particles thus is utilized toimpart a specific mechanical strength to the glass substrate.

Before this particle-fixing heat treatment cycle, the substrate can besubjected to a first heat treatment cycle to burn off the photosensitiveresin.

This first heat treatment cycle is especially advantageous since itcompletely prevents any “blistering” of the resin. This ensurespreservation of the integrity, and in particular the contours, of thepatterns after the heat treatments.

This secondary heat treatment is advantageously performed at atemperature on the order of 350° C., for a period of about 6 minutes perμm of thickness of the first layer. Depending on the desired type ofmodification of the appearance and/or structure of the bare transparentsubstrate, the mineral-particle-based composition can comprise a metalpowder and/or a ceramic powder and/or a metal-oxide-based powder and/orfunctional particles of the liquid-crystal or phosphorus-particle type.The metal powder can be silver, gold or ruthenium oxide powder.

The liquid crystals will be selected by one skilled in the art accordingto the color of the pattern to be produced, depending, for example, onthe nature of these crystals and the angle at which they are viewed bythe observer. In the case of a “mixed” powder comprising a metal powderwith a metal-oxide powder, the latter advantageously serves as a bindingagent.

When an ornamental appearance is the primary consideration, themineral-particle-based composition preferably comprises an enamelcomposition containing at least one glass frit.

The choice of the enamel composition is within the compass of thoseskilled in the art, who will adapt said composition depending on thesubstrate, particularly its nature and thickness.

In a known manner, the glass frit contains forming oxides to form theessential constituents of the vitreous material, modifying oxides ableto modify this vitreous matrix and capable of affecting the meltingpoint, and intermediate oxides that act as forming and/or modifyingoxides, depending on their environment and their proportions.

Based on the quantity of modifying oxides and on the ratios between theintermediate and the forming oxides, one skilled in the art will choosethe enamel composition having the temperature characteristics suited tothe invention.

According to an advantageous characteristic of the invention, the glassfrit includes the following constituents, in proportions by weight:

PbO 40-75% ZnO 0-7% Al₂O₃ 0-5% SiO₂  1-35% ZrO₂ 1-5% B₂O₃  0-10% K₂O  0-0.2% BaO   0-0.2% SrO   0-0.2%

According to a preferred variant of the invention, and when a decorativepattern formed by a visible image is desired, pigments, preferably of asingle color shade, are added to the enamel composition before it isdeposited.

In this preferred configuration, the enamel is used, astutely, as abinding agent. This is possible because the enamel creates a vitreousmatrix which is ideal for unifying the pigments with the glass substratein a durable manner.

According to the invention, it is preferable to add the pigments inproportions such that the ratio by weight between the glass frit and thepigments is between 50:50 and 90:10, preferably between 70:30 and 60:40,per 100 parts of frit-pigment mixture.

To obtain the best possible homogeneity between the pigments and theglass frit, the particle size of the pigments is advantageously selectedso that it is roughly equal to that of the glass frit. The diameter ofthe pigments [the pigment particles] is preferably less than 10 μm,particularly between 1 and 5 μm.

When a metallized appearance is desired for the decorative pattern, itis preferable for mica pigments to be the majority constituent.

When a very-high-definition polychrome image is desired, according tothe invention Steps a), b) and c) are performed n times in succession onthe same area, with the alternating deposition of a hydrophilic resinand a hydrophobic resin, the n enamel compositions being notable in thateach of them contains, as its majority constituent, black or whitepigments or pigments that impart a single color.

According to this variant, when a four-color image is desired (n=4), thefour enamel compositions together include black pigments as theirmajority constituent and impart the three primary colors each of themincluding as its majority constituent black pigments or pigments thatimpart only one of the three primary colors.

With regard to the formulation of the pigments, the white pigmentselected is preferably titanium oxide TiO₂.

Similarly, for pigments imparting the primary color blue (cyan), Co₃O₄pigments are advantageously selected. Finally, for pigments impartingthe primary colors red (magenta) and yellow, the preferable choice iscadmium oxide CdO pigments mixed with cadmium sulfoselenide pigments,the relative proportions of which are modulated to obtain one (red) orthe other (yellow) of the primary colors.

According to this same variant, the first photosensitive resin depositedis advantageously hydrophilic.

The invention relates not only to the method for producing thedecorative pattern described hereinabove, but also to a transparentsubstrate, particularly a glass or glass-ceramic substrate, comprisingon one of its faces at least one enameled area reproducing a decorativepattern.

This substrate is notable for the fact that in the enameled area it hasa strictly positive light transmission coefficient, particularly ofbetween 0.05 and 90% for an enameled layer with a thickness of less than10 μm, preferably less than 5 μm. Such a substrate is particularlyadvantageous because if the decorative pattern can be viewed from bothsides, its range of application is much broader than that of existingenameled substrates. Furthermore, the decorative pattern is visible froma very great distance.

The resolution of the decorative pattern is preferably higher than 15d.p.i. (dots per inch), advantageously higher than 150 d.p.i.

The decorative pattern can be a monochrome or polychrome visible image,particularly a four-color image, and when this is the case theresolution of the image is as stated in the foregoing. Such finenessenables the image to be viewed at a plurality of distances, which meansthat two observers disposed at different distances from the substratewill distinguish different details of the image.

The invention is applicable to the manufacture of any high-resolutiondecorative glass product, such as a glass-covered luminous sign, a glassoven door with an oven molding¹, a display window, an interiorpartition, a stained-glass window. The glass product according to theinvention can also be combined with another glass product by dividing itinto sheets to lend it specific properties. This other glass product canbe, for example, a transparent substrate coated with thin layers thatprovide it with a highly specialized functionality, such as anantireflective, non-fogging, or dirt-repelling function.

¹TRANSLATOR'S NOTE: French bandeau de cuisiniere. The term is unknown tous. “De cuisiniere” could also be translated as “cook's”; bandeau couldalso be “strip” or “band”.

The invention is also applicable to the manufacture of “fronts” foremittive screens in the nature of flat screens such as plasma screens.

A plasma screen is composed of two glass substrates superimposed on eachother, constituting the front and back of the screen.

Although the screen-printing technique is completely suitable in termsof precision for depositing the components of the “back”, and moreparticularly the luminophores and the silver-paste-based electrodes, itis not necessarily adequate for depositing the components of the front,by the very fact that these components must be disposed in virtuallyperfect opposite alignment with like elements on the back.

The high resolution provided by the aforesaid method of the invention,on the other hand, is perfectly adapted to this task.

For example, the technique according to the invention can be used todeposit, opposite each luminophore of the back, a selective coloredfilter of the desired wavelength produced from a ceramic powderoptionally mixed with a low-melting-point glass frit.

It is also possible to deposit silver-paste-based electrodes which mustbe absolutely perpendicular to those of the back.

Finally, to improve the luminous efficiency of the plasma screen,luminophores which were difficult to deposit heretofore can be depositedas readily in very fine layers on the front.

Other details and advantageous characteristics will emerge hereinafterfrom the following nonrestrictive example according to the invention.

A solution containing 120 g/liter of a photosensitive resin is preparedin inactinic light.

For this purpose, first, 150 g of the ethylene-glycol and butanediolpolycynamylidene malonate, with a density of d=1.237, are ground andthen dissolved in 1 liter of a first solvent containing, respectively,53% toluene, 21% butyl acetate and 26% 2-methoxyethyl acetate.

4.5 g of a sensitizer which is 1-N(methylbenzothiazolidene)methyldithiocetate are also ground and are then dissolved to saturation in asecond solvent containing 30% butyl acetate and 70% 2-methoxyethylacetate; the solution as a whole is then filtered and added to the firstsolvent.

A layer of this solution, which has a viscosity on the order of 28 Pa/s,is applied to a glass substrate, with a flexible brush, for example.

The average thickness of this layer of photosensitive resin is less than5 μm after drying for 30 min at 60° C. Some portions of thephotosensitive product obtained in this manner are exposed to light bymeans of a UV laser with about 1 kW of power, whose beam is deflectedpoint by point by a mirror to reproduce the desired visible image.

A second layer of an enamel composition is then applied uniformly overthe entire first layer of photosensitive resin, areas of which have beenexposed to light.

To make this composition, first, a cullet-based glass frit of a clearsoda-lime-silica glass is reground by the liquid method to yieldultrafine particles.

The particle size of the glass frit has been measured: diameters d₁₀,d₆₀ and d₉₀ are, respectively, 0.2 μm, 1.25 μm and 10 μm.

These finely ground particles are then mixed with titanium oxide TiO₂pigments with diameters d₁₀, d₆₀ and d₉₀ of, respectively, 0.4 μm, 2 μmand 7 μm, in proportions such that the weight ratio between the pigmentsand the glass frit is 48:52 per 100 parts of frit-pigment mixture.

The composition of the enamel, in proportions by weight, is as follows:42% PbO, 4.9% ZnO, 1.9% SiO₂, 1.4% ZrO₂, 0.9% Al₂O₃, 0.14% SrO and 48%TiO₂.

Finally, the combination of glass frit plus pigments so constituted ismixed with a medium which is alcohol.

Once this second layer of enamel composition has been applied, drying isperformed in an oven at 60° C. for 30 seconds, with evacuation of thealcohol vapors.

This is followed by washing in lukewarm water at a temperature on theorder of 50° C., accompanied by brushing of the second layer with asoft-bristled brush.

At the time of this washing step, the excess enamel not absorbed by thefirst layer of photosensitive resin is recovered by being decanted intoa container.

Finally, the substrate coated in this way is put through a heattreatment cycle. This is composed of burn-off of the resin at 350° C.for 1 hour, followed by baking of the enamel and quenching of the glasssubstrate at about 620° C.

The substrate obtained in this manner comprises an enameled area thatreproduces a very-high-definition visible monochrome image withresolution of 150 d.p.i. This excellent resolution is directly relatedto the focusing capacity of the laser beam, and is, in particular, onthe order of 10 μm.

Further, the gray levels in this enameled area have been calibratedarbitrarily from 0 to 21 and the light transmission coefficient of eachgray level has been measured. The values are given in the followingtable:

TABLE Gray Level Light Transmission Coefficient 1 87.1 2 56.2 3 38.0 426.3 5 17.8 6 12.6 7 8.9 8 5.9 9 4.3 10 2.9 11 2.1 12 1.5 13 1.1 14 0.715 0.5 16 0.40 17 0.28 18 0.22 19 0.15 20 0.10 21 0.07

This table makes it clear that the capacity of the image can be adjustedover a broad range, and thus that it is possible to obtain very markedcontrasts.

It goes without saying that many modifications of detail can be made inthe method described hereinabove without thereby departing from thescope of the invention.

For example, it is possible to modulate the devitrification of the glassfrit in such a way as to produce a color image without the need forpigments.

Similarly, the optional medium used to deposit the enamel composition onthe layer of photosensitive resin can be laid down before the depositionof the glass frit particles.

Finally, with regard to selective particle deposition, a secondselectivity in addition to that provided by the light source can befurnished by distributing particles uniformly over the entire surface.

What is claimed is:
 1. A substrate produced by: a) depositing on atleast part of a face of a substrate a first layer of a photosensitiveresin comprising (i) a sensitizing agent and (ii) at least onephotosensitive compound comprising a polymer with an average degree ofcross-linking d° such that it is able to absorb solid particles; b)exposing an area of said first layer to light to increase the averagedegree of cross-linking d° of said polymer, wherein the absorptioncapacity of the polymer is modulated as a function of light exposure; c)after exposure, depositing on said first layer a second layer of acomposition comprising mineral particles, wherein at least some of themineral particles are absorbed by the first layer; and d) subjectingsaid substrate to at least one heat treatment cycle, to fix said mineralparticles, wherein said substrate comprises a pattern having a shadingor gradation of color intensity.
 2. A high resolution decorative glasscomprising a substrate according to claim
 1. 3. The substrate of claim1, wherein said polymer is ethylene-glycol and butanediolpolycynamylidene malonate.
 4. The substrate of claim 1, wherein thediameter of the mineral particles is less than or equal to the thicknessof said first layer.
 5. The substrate of claim 4, wherein the diameterof said mineral particles d₉₀ is less than or equal to 10 μm.
 6. Thesubstrate of claim 5, wherein the diameter of said mineral particles d₉₀is between 4 and 8 μm.
 7. The substrate of claim 1, wherein saidcomposition comprising mineral particles is an enamel compositioncomprising at least one glass frit.
 8. The substrate of claim 7, whereinsaid enamel composition also includes pigments.
 9. The substrate ofclaim 8, wherein the particle size of the pigments is about equal to theparticle size of the glass frits.
 10. The substrate of claim 8, whereinthe diameter d₉₀ of the pigments is less than 10 μm.
 11. The substrateof claim 10, wherein the diameter d₉₀ of the pigments is between 1 and 5μm.
 12. The substrate of claim 8, wherein the weight ratio between theglass frit and the pigments is between 50:50 and 90:10, per 100 parts offrit-and-pigment mixture.
 13. The substrate of claim 12, wherein theweight ratio between the glass frit and the pigments is between 70:30and 60:40, per 100 parts of frit-and-pigment mixture.
 14. The substrateof claim 7, wherein said enamel composition includes mica pigments asits majority constituent.
 15. The substrate of claim 1, wherein themineral particles are uniformly applied to the substrate.
 16. Thesubstrate of claim 1, wherein the pattern contains no trace of gridding.17. The substrate of claim 1, wherein the heat treatment temperature isgreater than or equal to the melting temperature of at least a portionof the mineral particles.